Electrolytes form a crucial part of electrochemical and/or optoelectronic devices and performance of the device largely depends on the physical and chemical properties of the various components of these electrolytes.
Amongst solar cells, those sensitised with a dye or quantum dots for example, have been paid intensive attentions in the last 15 years as an alternative to silicon technology and progresses have been made in the development of efficient dyes, electrolytes and TiO2 films to enhance the device performance.
Encapsulation and leakage of high vapor pressure organic solvents based electrolytes is a major challenge for the commercialization of many electrochemical and/or optoelectronic devices and in particular sensitized solar cells. Room temperature ionic liquids are attractive candidates to replace volatile organic solvents present in such devices due to their negligible vapor pressure and high ionic conductivity.
Imidazolium iodide ionic liquids, for example, are very viscous and the high concentration of iodide ions in these electrolytes creates a loss channel through reductive quenching of the excited sensitizer, hampering device performance. Use of binary ionic liquid electrolytes for sensitized solar cells reduces both the viscosity of the electrolyte and the reductive quenching effect. Various binary ionic liquid electrolytes have recently been applied to dye-sensitised solar cells reaching over 7.0% photovoltaic conversion efficiency with a good stability under accelerated light soaking tests at 60° C. However, the drawback of the anions thiocyanate, selenocyanate, dicyanamide and tricyanomethanide that have been used along with iodide to attain such an impressive performance is their thermal instability resulting in photovoltaic performance loss under prolonged thermal stress at 80° C.
In view of the above, it is an objective of the present invention to provide electrolytes for electrochemical and/or optoelectronic devices that may lead to improved performance of these devices. Furthermore, it is an objective to increase thermal stability of such devices and in particular sensitised solar cells.
It is a further objective to reduce the quantity of iodide ions in electrochemical and/or optoelectronic devices. Disadvantages of iodide ions are, for example, the high viscosity and low efficiency of electrolytes containing them.
It is a more general objective of the present invention to provide new electrolytes or new electrolyte components that can be advantageously used in these devices. Ionic liquids with negligible vapour pressure are known as “green solvents” due to their non-toxicity. It is thus an objective of the invention to use them as electrolytes in optoelectronic devices to make them environmentally friendly.